As part of #90752, we need to add support to the allocator to be able to evaluate the viability of node decommission, by validating that we have valid upreplication targets for all replicas on the node we intend to decommission. In order to do this, we need to add allocator support for determining actions and allocation targets with states not currently represented in the StorePool.

Part of #91570.

Jira issue: CRDB-21321